The present disclosure relates generally to synchronization in software-defined radio systems, and more specifically to alignment of data signal samples in sample streams from radio receivers of such systems.
Software-defined radio (SDR) systems are radio communications systems in which various functions that are usually implemented in hardware in radio systems can instead be performed by software in some form of data processing system connected to the radio receivers. Radio signals can be analysed and demodulated entirely in software running on general purpose processors, without the need for specialized decoding radio hardware. This allows for higher flexibility with respect to new communication protocols and lower complexity in the radio front-end infrastructure. Software defined radio is already in use in many communication applications to speed-up technology development and to allow for adaptable system designs. A typical SDR system, such as a C-RAN (Cloud Radio Access Network) system may include a distributed array of fixed radio receivers connected via a network to a centralized data processing system such as a cloud computing system. The radio receiver (or “radio head”) units can receive data signals transmitted in their receiving band by devices in their neighborhood, and generally also transmit to such devices. The front-end receiver hardware converts received radio signals to digital sample streams which are sent via the network to the back-end processing. Signal processing tasks such as modulation/demodulation, signal detection, encryption/decryption, etc., can be efficiently performed by SDR processing resources in the back-end, allowing simplification of front-end receivers.
Current SDR architectures require precise time synchronization at the radio receivers and dedicated network links with transport time information for transporting signals to the back-end processing. The receiver clocks are synchronized, e.g. using GPS (Global Positioning System) hardware, for alignment, or synchronization, of samples in the sample streams from different receivers. The timing information provided by specialized transport-network hardware allows synchronization between receivers and SDR processing in the back-end. As well as signal alignment, this clock synchronization is required for processes such as device localization in which geographical location of a data transmitter is determined from the time-difference-of-arrival (TDOA) of the data signal at known receiver locations.